1. Technical Field
Exemplary aspects of the present disclosure generally relate to an image forming apparatus including an intermediate transfer member.
2. Related Art
Image forming apparatuses using electrophotography and employing intermediate transfer are well known. In such image forming apparatuses using an intermediate transfer method, for example, multiple toner images are sequentially formed on an image carrier such as a photoreceptor drum. The multiple toner images are then sequentially superimposed on each other in a primary transfer to a rotationally moving intermediate transfer member. A composite toner image formed of the multiple toner images on the intermediate transfer member is transferred in a secondary transfer to a recording sheet such as a transfer paper that is a recording medium.
Image forming apparatuses using the intermediate transfer method have certain advantages, such as being easy to downsize and little restriction on the type of recording medium used. Thus, these image forming apparatuses are frequently used for color image forming apparatus.
There are image forming apparatuses using a type of intermediate transfer method that includes a secondary transfer roller forming a secondary transfer nip with the intermediate transfer member, and a mechanism for contacting and separating the secondary transfer roller to and from the intermediate transfer member.
For example, a related art describes an image forming apparatus including a secondary transfer opposing roller provided opposite the secondary transfer roller to support an intermediate transfer belt serving as the intermediate transfer member from the back, and a cam member provided on the same axis of the secondary transfer opposing roller to contact a follower (a free rotation roller) provided on the same axis of the secondary transfer roller.
In the above-described image forming apparatus, a protruding portion of the cam member contacts the free rotation roller before the recording sheet enters the secondary transfer nip. By the contact of the protruding portion of the cam member to the free rotation roller of the secondary transfer roller, the secondary transfer roller that is pressed toward the intermediate transfer belt is separated from the intermediate transfer belt. As a result, a space is formed in the secondary transfer nip between the secondary transfer roller and the intermediate transfer belt and is maintained. Just before the recording sheet enters the secondary transfer nip, the cam member is rotated to a position at which the protruding portion of the cam member does not contact the free rotation roller of the secondary transfer roller.
As a result, generation of a load change is prevented due to the slight space in the secondary transfer nip when a front end of the recording sheet enters the secondary transfer nip. The space is eliminated immediately after the recording sheet enters the secondary transfer nip. Accordingly, the recording sheet is reliably sandwiched in the secondary transfer nip, and reliable secondary transfer of a toner image is realized. The above configuration is particularly effective in a case in which the recording sheet that is being passed through is relatively thick (hereinafter referred to as thick recording sheet). The generation of load change and vibration due to the impact of the recording sheet striking the intermediate transfer belt and the secondary transfer roller when the front end of the thick recording sheet enters is reduced and hence a good toner image is produced.
However, in conventional image apparatuses with the intermediate transfer method that includes the above-described mechanism, a start timing of the rotation of the cam member in a direction in which the protruding portion of the cam member does not contact the free rotation roller (eliminates the space in the secondary transfer nip) is constant upon the entry of the recording sheet into the secondary transfer nip.
Accordingly, if the cam member starts to rotate to provide an appropriate space for the thick recording sheet upon entry into the secondary transfer nip, the space upon entry into the secondary transfer nip is too large when the recording sheet is relatively thin (hereinafter referred to as thin recording sheet) or is a normal sheet of paper. Thus, when the separation of the secondary transfer roller and the intermediate transfer belt is cancelled, a return shock occurs to both the secondary transfer roller and the intermediate transfer belt. The return shock generates load change and vibration, resulting in image failure.